The new and promising method for measuring the topographic distribution of water in lung tissue is proposed. This method is based on reconstructing or imaging the three-dimensional water concentration by nuclear magnetic resonance (NMR) techniques. By control of externally applied moderate strength static magnetic fields with small gradient components and radio-frequency (RF) electromagnetic fields, the spatial distribution of water protons and other hydrocarbons may be determined by detection of the associated NMR interactions. The proposed method is highly sensitive to and selective water concentration, and therefore promises to provide the first quantitative noninvasive determination of relative and absolute water concentration in tissues. Unlike X-ray methods which produce cumulative tissue damage due to ionization effects, the NMR methods are nonionizing and produce no known adverse side effects (except possibly at extremely high and difficult-to-obtain power levels). This technique promises to provide the first fundamental standard for the in vivo quantitative measurement of lung water. An NMR system will be constructed and then used to measure lung water and its distribution in pulmonary edema. Because of its sensitivity, rapidity, and nonivasiveness, NMR promises to give a detailed account of the time course and regional development of lung edema.